This invention relates generally to apparatus for logging inclined earth boreholes and specifically to apparatus utilizing mutually independent arm pad assemblies in such boreholes.
It has become relatively common within the last few years to drill wells in the search for oil and gas and the like with a portion of the bore deviating from the usual vertical orientation thereof. The deviation or inclination may extend for a considerable distance at angles ranging to 70.degree., sometimes returning to the usual vertical orientation.
It is also well known in the art of drilling such deviated wells that the borehole becomes egg-shaped rather than round and that when logging such egg-shaped boreholes with an instrument having a plurality of arm pads, one or more of the pads tends not to be in contact with the borehole wall.
The four-arm instruments commonly used in the art have two opposite arms working independently of the other two opposite arms. Generally speaking, one pair of opposite arms will be powered by a single force, for example, a spring, and the other pair are powered by a separate single force for example a second spring.
As will be shown hereinafter by reference to the figures of the drawing, regardless of whether one uses weak or strong springs, one of the pads on one of the arms will lift off the borehole wall by some distance and thus produce an inaccurate log of the well.
It is therefore a primary object of the present invention to provide a new and improved apparatus for logging earth boreholes;
It is also an object of the present invention to provide new and improved apparatus for logging highly deviated boreholes; and
It is still another object of the present invention to provide new and improved apparatus having a plurality of arm pad members and having means for causing each of the pad members to remain in contact with the borehole wall even whenever such borehole wall becomes irregular.
The objects of the invention are accomplished, generally, by a borehole logging instrument having separate force means driving each of a plurality of arm pad members against the borehole wall. As an additional feature of the invention, the individual arm pad members are closed to facilitate traversal of the earth borehole while either going into the borehole or pulling the borehole instrument out of the well.